Add test-debug label to run PR tests with verbose pytest logging (DataDog#24436)

Some integrations (e.g. kong) only build/run on amd64, so their E2E tests
can't be run locally on non-amd64 dev machines to inspect debug output such
as discovery candidate probing. Setting the "test-debug" label on a PR now
passes -rP --log-level=DEBUG to pytest via the existing pytest-args input,
surfacing that output in the CI job log instead.

Environment: Datadog workspace

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com> 2042232

Author: pull[bot]